Advances in medical care have improved rates of survival of very low birth weight (VLBW) premature infants (<1.5kg). However, increased survival rates have been accompanied by a significant increase in the number of survivors with reduced cerebral growth and long-term neurodevelopmental motor, cognitive, and social morbidities. There is a critical need for a means of precise identification of the functional nature of these morbidities, to guide the earliest possible behavioral interventions that leverage neural plasticity. A candidate morbidity is force modulation and planning in the use of the hands. This project uses innovative flexible electronic sensor technology embedded in soft materials worn on the hands along with motion capture to examine how children plan and modulate forces during block construction, tool use, and social play. Longitudinal measurement of group differences in force modulation and planning between toddlers born prematurely and typically developing children will make it possible to determine the safety and effectiveness of this innovative sensor technology for early assessment of morbidities due to premature birth. The research leverages work at Harvard on the use of liquid circuits fabricated in soft materials (elastomers) that bend and stretch as they conform to the hands. The outcome will be a new type of device comfortably worn on the hands of toddlers, called flexi-mitts. Design and fabrication of flexi-mitts present several technical challenges, including (a) embedding the circuitry in multiple layers of material, (b) circuit architectures precisely scaled and spatially arranged to provide measurements of joint angles of the fingers as well as bending torques, (c) simultaneous measurement of finger and wrist joint angles, (d) incorporation of wireless, battery-powered technologies, and (e) circuit architectures that are simplified to fit the form factor of the tiny hands of toddlers. This new flexi-mitt technology has the potential to provide a new diagnostic tool for precise, non-invasive measurement of the effects of premature birth on force modulation and planning. RELEVANCE (See instructions): There is a critical need for diagnostic tools that identify more precisely the nature of developmental delays in prematurely born children. Our project develops flexible electronic sensors embedded in soft materials, called flexi-mitts, worn on the hands of toddlers to measure planning during play at ages 18, 24, and 30 months. The results will provide the foundation for a new assessment tool.